In a conventional SAW device, after a metallic thin film has been formed on a whole surface of a piezoelectric substrate, a resist is coated on the metallic thin film and then, a desired electrode pattern is formed in which desired interdigital transducers and grating reflectors are not only surrounded by dicing lines but connected by thin lines through exposure, development and etching. The thus obtained article is cut along the dicing lines into a plurality of the SAW devices.
In this method, once the SAW device has been cut from the piezoelectric substrate, the interdigital transducers and the grating reflectors are electrically separated from each other. Hence, upon application of heat or strain to the SAW device, electric charge is generated by pyroelectric property of the piezoelectric substrate. Thus, if electric charge becomes nonuniform among the electrodes, electric discharge occurs between the confronting interdigital transducers, between the confronting grating reflectors and between the interdigital transducer and the grating reflector, thereby resulting in damage to the electrodes or deterioration of characteristics of the SAW device.
On the other hand, a method for solving this problem is known from Japanese Patent Laid-Open Publication No. 11-298289 (1999). Namely, since inside a dicing line, a short-circuiting thin line of a metallic thin film surrounds an interdigital transducer and a grating reflector and a plurality of thin lines are provided for electrically connecting the short-circuiting thin line of the metallic thin film and the interdigital transducer are provided, generated electric charge is uniformized electrically, so that damage and deterioration of electrical characteristics due to electrostatic discharge are prevented.
However, in this conventional arrangement in which inside the dicing line, the short-circuiting thin line of the metallic thin film surrounds the interdigital transducer and the grating reflector and the thin lines electrically connect the short-circuiting thin line of the metallic thin film and the interdigital transducer, such disadvantages are incurred that since generated electric charge cannot be neutralized and uniformized sufficiently due to rise of impedance between lines in case the generated electric charge is large, in case a distance between the electrodes is short, in case the connected electrodes are far from each other, the line for connecting the short-circuiting thin line of the metallic thin film and the interdigital transducer is thin or in case the connecting line is a meander line or a portion of the connecting line is thinner than the remaining portion of the connecting line, damage to the electrodes and deterioration of electrical characteristics are caused by electrostatic discharge generated between the electrodes.